Polynetwork EPDM rubber

Abstract

Polynetwork EPDM rubber is EPDM rubber containing both ionomeric and covalent cross-links, and can be formed by treating EPDM rubber with maleic acid or anhydride or fumaric acid to attach succinic groups to the rubber, forming an ionomer thereof with a polyvalent metal oxide, hydroxide or salt, and then covalently cross-linking the rubber, for example, by sulfur vulcanization. Compositions are shown containing the polynetwork rubber in combination with oil and black, optionally in blends with high-diene hydrocarbon rubber, such as natural rubber.

We claim: 
     
       1. Polynetwork rubber which rubber is a product of the polymerization of a mixture of ethylene, propylene and a lesser quantity of non-conjugated diene, said rubber containing both ionomeric cross-links and cross-links formed by the reaction of said rubber with sulfur or a sulfur donor, a methylol phenolic resin or an organic peroxide. 
     
     
       2. The polynetwork rubber of claim 1 in which the ionomeric cross-links are based on the neutralization of succinic groups pendent to the rubber molecules, by metal oxide, metal hydroxide, or salt of a weak acid. 
     
     
       3. Polynetwork rubber which rubber is a product of the polymerization of a mixture of ethylene, propylene and a lesser quantity of non-conjugated diene formed by (A) treating the polymerization product with maleic acid or anhydride or fumaric acid to form an adduct,   (B) treating the adduct thus formed with a polyvalent metal salt, hydroxide or oxide to form an ionomer, and   (C) cross-linking the ionomer with a vulcanizing agent selected from sulfur or sulfur donors, methylol phenolic resins and organic peroxides so as to introduce covalent cross-links therein, in which the steps can be sequential or simultaneous.   
     
     
       4. The polynetwork rubber of claim 3, wherein (A) the polymerization product is treated by mastication with maleic anhydride to form the adduct,   (B) the adduct is treated with zinc oxide to form the ionomer and   (C) the ionomer is cross-linked with a vulcanizing agent selected from sulfur, sulfur donors, methylol phenolic resin and an organic peroxide, wherein the non-conjugated diene is selected from 1,4-hexadiene, cyclooctadiene, ethylidenenorbornene and dicyclopentadiene.   
     
     
       5. The polynetwork rubber of claim 4, wherein a free-radical generator is present during step (A). 
     
     
       6. The rubber of claim 5 wherein the free-radical generator is benzothiazyl disulfide. 
     
     
       7. A composition comprising the polynetwork rubber of claim 1, and from 5 to 500 parts by weight, based on the rubber, of a high-diene hydrocarbon rubber. 
     
     
       8. A composition comprising the polynetwork rubber of claim 1, and from 0 to 200 parts by weight, based on the rubber, of carbon black. 
     
     
       9. A composition comprising the polynetwork rubber of claim 1, and from 0 to 200 parts by weight, based on the rubber, of a rubber processing oil. 
     
     
       10. A composition comprising the polynetwork rubber of claim 2, and from 0 to 200 parts by weight each, based on the rubber, of carbon black and a rubber processing oil. 
     
     
       11. A composition according to claim 7 and from 10 to 200 parts by weight each, based on the total weight of the polynetwork rubber plus the high-diene hydrocarbon rubber, of carbon black and a rubber processing oil. 
     
     
       12. The polynetwork rubber of claim 1, wherein the ionomeric cross-links comprise N-carboxyalkyl- or N-carboxylaryl-substituted succinamic acid or succinimide groups.